This invention relates to an improved photoconductive film of electrophotographic photoconductors used for printers and copying machines which employ electrophotographic processes. More specifically, this invention relates to constituent materials of the photoconductive film.
Conventional photosensitive materials of the electrophotographic photoconductor (hereinafter simply referred to as a "photoconductor" used for the printers, facsimile machines, digital copying machines and analog copying machines) employed in electrophotographic processes include inorganic photoconductive materials such as selenium, selenium alloys deposited by vacuum deposition zinc oxide and cadmium sulfide dispersed into resin binder, organic photoconductive materials such as poly-N-vinylcarbazole, poly(vinyl anthracene), phthalocyanine compounds and bisazo compounds dispersed into resin binder or deposited by vacuum deposition.
It is required that the photoconductor retain surface charges in the dark, generate electric charges in response to the received light, and transport electric charges in response to the received light. The photoconductor may be classified into either the mono-layered-type, that exhibits the above described functions using one single photoconductive film, or the so-called laminate-type, that consists of one layer mainly for charge generation and another layer for charge retention in the dark and for charge transport in response to the received light. The electrophotographic techniques for image formation using the aforementioned types of photoconductors include the Carlson's process. The Carlson's process for image formation includes charging of the photoconductor by corona discharge in the dark, formation of electrostatic latent images of the letters and figures in a manuscript on the charged surface of the photoconductor, development of the electrostatic latent images with toner, and fixing of the developed toner images on a paper or other such carriers. The photoconductor is used again after charge removal, residual toner removal and optical charge removal.
Various image formation steps are employed in the Carlson's process. The corotron method or the scorotron method that uses metal wire and the contact charging method that uses the charging brush or charging roller are used for charging the photoconductor. The two-component development method, nonmagnetic-single-component development method, and magnetic-single-component development method may be used in the development step.
Recently, organic photoconductors have been developed by virtue of the flexibility, thermal stability and ease of film formation thereof. U.S. Pat. No. 3,484,237 discloses a photoconductor that includes poly-N-vinyl carbazole and 2,4,7-trinitrofluorenone. Japanese Unexamined Laid Open Patent Application No. S47-37543 discloses a photoconductor that includes an organic pigment as the main component thereof. Japanese Unexamined Laid Open Patent Application No. S47-10785 discloses a photoconductor that includes an eutectic complex consisting of a dye and resin as the main component thereof. At present, the function-separation-type organic photoconductors, which include a charge generation layer and a charge transport layer, are mainly used. The charge generation layer comprises metal-free phthalocyanine, metal phthalocyanine such as titanyl phthalocyanine or azo compound and a resin binder. The charge transport layer contains a hydrazone compound, styryl compound, diamine compound or butadiene compound and a resin binder.
Although the organic photoconductive materials have many advantages over inorganic photoconductive materials, the conventional organic photoconductive materials do not exhibit all the properties required of an electrophotographic photoconductor. It is desired to obtain a highly sensitive photoconductor that exhibits little change in the properties thereof after the photoconductor is continuously used in the electrophotographic apparatus for a long time. The aforementioned capability is especially important because of the customer's increasing demand for photoconductors which are durable enough to endure long continuous use in various electrophotographic devices using the foregoing imaging processes. The photosensitivity of the conventional laminate-type photoconductors are insufficient. Practical long use of the conventional laminate-type photoconductors causes charge potential lowering, residual potential rise, sensitivity lowering, and such problems have yet to be solved. Thus, there is a need for a technology that facilitates realizing all the favorable properties for the electrophotographic photoconductor.
In view of the foregoing, it is an object of the invention to provide an electrophotographic photoconductor that is stable enough to endure repeated continuous use for an extended time in practical electrophotographic devices. It is another object of the invention to provide an electrophotographic photoconductor that is fully adaptable to various electrophotographic devices which employ the corotron method or the scorotron method that uses metal wire for charging, which employ the contact charging method that uses the charging brush or charging roller for charging, which employ the two-components-development method, which employ the nonmagnetic-single-component development method and which employ the magnetic-single-component development method.